The present invention relates to a method and apparatus useful in the production of drawn and ironed seamless metal cans.
One type of widely used container is known as a "two-piece can" and consists of a one-piece seamless metal shell and a top. Such two-piece cans are widely used for beverages and food products and may be made of aluminum, tin-plated steel or other metals.
A widely used process to produce the can shells, which are deep seamless container bodies, from flat sheets or disks is known as the "D and I", or drawing and ironing process. In the drawing and ironing process the blank sheet, for example, a flat sheet metal blank, is drawn into a shallow cup form in one or more drawing operations using a punch mounted on a press and a drawing die. Subsequently the shallow cup is processed through ironing operations, for example, ironing dies in the form of ironing rings in which the sidewall of the cup is progressively thinned and elongated. The ironing dies, by thinning the sidewall of the drawn cup, cause a flow of the metal away from the base of the cup, thereby increasing its height while the thickness of the cup bottom remains substantially unchanged.
The drawing and ironing process has been widely used to produce seamless shells, and many patents have issued in the United States and abroad directed to the process and machines used to produce such shells. Among such prior patents are American Can Company's prior U.S. Pat. No. 3,670,543 entitled "Drawing and Ironing Process" and U.S. Pat. No. 3,360,157 entitled "Method of Forming A Coated Metal Container and Artical Produced Thereby."
It is of great importance in the drawing and ironing process that the shells be properly lubricated and cooled during the processing steps. The process requires that the shells be produced and conveyed at very high speeds, for example, 300 shells per minute in a single production unit, in order for the process to be economically feasible. If the shells are not properly cooled or lubricated, they may bind, i.e., become stuck, in the ironing ring and on the punch and the rings may be quickly worn out. The ironing process, since it involves a flow of metal and friction, produces a considerable amount of heat. Such heat, unless removed by cooling fluid, would cause contraction of the metal ironing rings, causing the rings to be damaged or to be of an improper size, and further may bind a shell in the ring or on the punch.
It is presently known, consequently, that a coolant and lubricant, consisting of an oil-in-water emulsion, should be flooded onto the can shells before and while they are being ironed in the ironing rings. The materials used for the oil-in-water emulsion, since they must resist breakdown under high pressure, may be relatively expensive organic compounds. Furthermore, since the rate of production is desired to be very high, a considerable quantity of the emulsion is required to be flooded onto the can shells.
The can shells, subsequent to their emergence from the ironing rings, are cut to the proper height in a trimming operation. The can shells are conveyed from the last ironing ring to the trimming station by means of a conveyor belt or other conveyor system. A large quantity of the dragged out waste emulsion falls from the cans while being conveyed between the last ironing ring and the trimming operation and while being conveyed to the can washer. Subsequent to the trimming operation, the cans are washed and the surfaces prepared for subsequent processing using chemicals and water in a can washer. However, a relatively expensive operating process must be used in the can washer since the can's surface must be freed of the emulsion remaining on them from the ironing process to make them satisfactorily processable in subsequent operations.
The waste emulsion, which is the emulsion which is dripped from the cans, contains the lubricant oil, the water phase of the oil-in-water emulsion, and dirt or soil which has been carried along with the emulsion. This emulsion has been considered a costly waste and presents a problem in pollution control. Since a large quantity of the emulsion must be used for cooling, the amount of such waste emulsion is considerable. With increased emphasis on environmental control, and particularly on the quality of the water which is removed from the factory to the environment, it is necessary to treat the waste. The required pollution control equipment, because of the large volume of waste treated, may be both relatively expensive to install and operate.